Flexible bag having a drawtape closure

FIELD OF THE INVENTION

Flexible bags of the type commonly utilized for the containment and disposal of various household materials.

BACKGROUND OF THE INVENTION

Flexible bags, particularly those made of comparatively inexpensive polymeric materials, have been widely employed for the containment and disposal of various household materials such as trash, lawn clippings, leaves, and the like.

As utilized herein, the term “flexible” is utilized to refer to materials which are capable of being flexed or bent, especially repeatedly, such that they are pliant and yieldable in response to externally applied forces. Accordingly, “flexible” is substantially opposite in meaning to the terms inflexible, rigid, or unyielding. Materials and structures which are flexible, therefore, may be altered in shape and structure to accommodate external forces and to conform to the shape of objects brought into contact with them without losing their integrity. Flexible bags of the type commonly available are typically formed from materials having consistent physical properties throughout the bag structure, such as stretch, tensile, and/or elongation properties.

A common method of utilizing such bags is as a liner for a container such as a trash can or bin. It is often difficult to pull the top of a bag over the rim of the trash can or bin so that the bag stays in place in the trash can or bin. Materials are placed in the bag until the bag is filled to the capacity of the bag and/or container, or until the bag is filled to the desired level. When the bag is filled to capacity, or even beyond capacity due to placing additional materials above the uppermost edge of the bag, it is often difficult for the consumer to achieve closure of the bag opening since little if any free material remains to achieve closure of the bag opening above the level of the contents. If the filled bag is then set upon the floor by itself, another issue frequently encountered is a shifting of the bag contents which causes an imbalance within the bag and a corresponding opening of the closure of the bag with potential spillage of the contents.

Accordingly, it would be desirable to provide a flexible bag which is easier to place securely over the rim of the trash can or bin, which is easier to close when filled and which resists reopening when closed.

SUMMARY OF THE INVENTION

A flexible bag comprising at least one sheet of flexible sheet material assembled to form a semi-enclosed container having an opening defined by a periphery, said opening defining an opening plane, said bag having a drawtape closure for sealing said opening to convert said semi-enclosed container to a closed container, an upper region adjacent to said drawtape closure and a lower region below said upper region, wherein the sheet material of said drawtape closure exhibits an elastic-like behavior along at least one axis, the sheet material of said drawtape closure comprising: at least a first region and a second region, said first region and said second region being comprised of the same material composition and each having an untensioned projected pathlength, said first region undergoing a substantially molecular-level deformation and said second region initially undergoing a substantially geometric deformation when said web material is subjected to an applied elongation in a direction substantially parallel to said axis in response to an externally-applied force upon the sheet material of said drawtape closure, said first region and said second region substantially returning to their untensioned projected pathlength when said applied elongation is released.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

<figref idrefs="DRAWINGS">FIG. 1</figref> is a plan view of a flexible bag in accordance with one embodiment of the present invention in a closed, empty condition;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a perspective view of the flexible bag of <figref idrefs="DRAWINGS">FIG. 1</figref> in a closed condition with material contained therein;

<figref idrefs="DRAWINGS">FIG. 3A</figref> is a segmented, perspective illustration of the polymeric film material of flexible bags of one embodiment of the present invention in a substantially untensioned condition;

<figref idrefs="DRAWINGS">FIG. 3B</figref> is a segmented, perspective illustration of the polymeric film material of flexible bags according to one embodiment of the present invention in a partially-tensioned condition;

<figref idrefs="DRAWINGS">FIG. 3C</figref> is a segmented, perspective illustration of the polymeric film material of flexible bags according to one embodiment of the present invention in a greater-tensioned condition;

<figref idrefs="DRAWINGS">FIG. 4</figref> is a plan view illustration of another embodiment of a sheet material useful in the present invention; and

<figref idrefs="DRAWINGS">FIG. 5</figref> is a plan view illustration of a polymeric web material of <figref idrefs="DRAWINGS">FIG. 4</figref> in a partially-tensioned condition similar to the depiction of <figref idrefs="DRAWINGS">FIG. 3</figref> B.

<figref idrefs="DRAWINGS">FIG. 6</figref> is a side view illustration of a portion of a drawtape according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Flexible Bag Construction:

<figref idrefs="DRAWINGS">FIG. 1</figref> depicts one embodiment of a flexible bag <b>10</b> according to the present invention. In the embodiment depicted in <figref idrefs="DRAWINGS">FIG. 1</figref>, the flexible bag <b>10</b> includes a bag body <b>20</b> formed from a piece of flexible sheet material folded upon itself along fold line <b>22</b> and bonded to itself along side seams <b>24</b> and <b>26</b> to form a semi-enclosed container having an opening along edge <b>28</b>. Flexible bag <b>10</b> also includes drawtape closure <b>30</b> located adjacent to edge <b>28</b> for sealing edge <b>28</b> to form a fully-enclosed container or vessel as shown in <figref idrefs="DRAWINGS">FIG. 1</figref>. Bags such as the flexible bag <b>10</b> of <figref idrefs="DRAWINGS">FIG. 1</figref> can be also constructed from a continuous tube of sheet material, thereby eliminating side seams <b>24</b> and <b>26</b> and substituting a bottom seam for fold line <b>22</b>. Flexible bag <b>10</b> is suitable for containing and protecting a wide variety of materials and/or objects contained within the bag body.

In the configuration depicted in <figref idrefs="DRAWINGS">FIG. 1</figref>, the drawtape closure <b>30</b> completely encircles the periphery of the opening formed by edge <b>28</b>. However, under some circumstances a closure means formed by a lesser degree of encirclement (such as, for example, a closure means disposed along only one side of edge <b>28</b>) may provide adequate closure integrity.

Flexible bag <b>10</b>, in accordance with one embodiment of the present invention, includes region <b>31</b> adjacent to the closure <b>30</b> which is adjacent to the edge <b>28</b>. The drawtape closure exhibits a lower resistance to elongation than the region <b>31</b>.

<figref idrefs="DRAWINGS">FIG. 1</figref> shows a plurality of regions extending across the drawtape closure surface. Regions <b>40</b> comprise rows of deeply-embossed deformations in the flexible sheet material of the bag body <b>20</b>, while regions <b>50</b> comprise intervening undeformed regions. As shown in <figref idrefs="DRAWINGS">FIG. 1</figref>, the undeformed regions have axes which extend across the material of the bag body in a direction substantially parallel to the plane (axis when in a closed condition) of the open edge <b>28</b>, which in the configuration shown is also substantially parallel to the plane or axis defined by the bottom edge <b>22</b>.

In one embodiment the sheet materials are oriented such that their elongation axis in the upper portion of the bag is generally substantially perpendicular to the plane defined by the opening or open edge of the bag. This orientation provides the defined stretch orientations of one embodiment of the present invention. In one embodiment the sheet materials are oriented such that the elongation axis of the drawtape closure is parallel to the plane defined by the opening or open edge of the bag.

It is possible to construct substantially the entire bag body from a sheet material having the structure and characteristics of the embodiments of the present invention. It may be desirable under certain circumstances to provide such materials in only one or more portions or zones of the bag body rather than its entirety. For example, a band of such material having the desired stretch orientation could be provided in one region of the bag forming a complete circular band around the bag body to provide a more localized stretch property. In one embodiment, the band of material comprising the drawtape closure portion of the bag may have the structure and characteristics described herein.

In one embodiment, the first and second regions are formed only in the drawtape closure portion of the bag. This localized formation of the first and second regions may selectively enable the drawtape portion of the bag to be expanded in circumference relative to the remainder of the bag <b>10</b>. This relative expansion may enable a user of the bag <b>10</b> to more easily enclose the periphery of a container adapted to support the bag <b>10</b> to facilitate the filling of the bag <b>10</b>.

The selective formation of the first and second regions in the area of the drawtape closure may additionally yield a benefit of a closure which is more resistant to opening when a filled bag has been closed and subsequently removed from a supporting container than a similar bag lacking the modified drawtape closure would be. Without being bound by theory, it is believed that there is a ratchet effect present in the mechanical interaction between the formed regions of the draw tape and the formed regions of the sheet material as well as an additional ratchet effect between the regions of the respective portions of the sheet material surrounding the draw tape.

The ratchet effect may be achieved by forming the first and second regions in the draw tape and the surrounding hem material, or in either the draw tape or the surrounding hem material alone. Each of the draw tape and the surrounding hem material may be either continuously or selectively formed into first and second regions. By selectively formed it is meant that discrete portions of the material may have first and second regions formed and other portions may have no such regions formed. Such selective formation of first and second regions may achieve a selective ratchet effect wherein the greater resistance to opening is more prevalent in particular preselected portions of the draw tape.

In one embodiment each of the draw tape and the surrounding hem material may comprise a different pattern of first and second regions in order to facilitate the interaction of the regions of the draw tape with those of the surrounding hem material.

In one embodiment illustrated in <figref idrefs="DRAWINGS">FIG. 6</figref>, the draw tape <b>30</b> may further comprise one or more looped sections wherein the tape is formed into a series of crests <b>32</b> and troughs <b>34</b> where each trough <b>36</b> of a looped section is sealed to an elastomeric strip <b>36</b> corresponding to each looped section. This allows the drawtape <b>30</b> to be extended such that exposed portions of the drawtape <b>30</b> may be used to secure the tape and the top of the bag over the lip of a bag holding container.

In one embodiment the drawtape may further comprise an elastomeric material such as a thermoplastic rubber compound blended with a polyolefin.

In any of the embodiments, the draw tape, the surrounding hem material, or both may be embossed such that a pattern is present in the material but the first and second regions having differing responses to the application of a force along an axis of the pattern are not formed. Bags formed with such embossed draw tapes and/or hem material may still undergo the ratchet interaction between the embossed pattern of the material and the other components of the draw tape closure.

The draw tape may comprise a polymer substantially similar to that of the sheet material or may comprise a dissimilar polymer material. The sheet material may be modified to include the first and second regions either prior to or subsequent to the addition of the draw tape to the bag <b>10</b>. Modification of the sheet material subsequent to the addition of the draw tape may include modification of the draw tape to include first regions and second regions as well. In one embodiment, the sheet material including the hem seal formed to constrain the motion of the draw tape, and the draw tape may be modified concurrently using the method described below.

Materials suitable for use in the embodiments of the present invention, as described hereafter, are believed to provide additional benefits in terms of reduced contact area with a trash can or other container, aiding in the removal of the bag after placing contents therein. The three-dimensional nature of the sheet material coupled with its elongation properties also provides enhanced tear and puncture resistance and enhanced visual, aural, and tactile impression. The elongation properties also permit bags to have a greater capacity per unit of material used, improving the “mileage” of such bags. Hence, smaller bags than those of conventional construction may be utilized for a given application. Bags may also be of any shape and configuration desired, including bags having handles or specific cut-out geometries.

To better illustrate the structural features and performance advantages of flexible bags according to the embodiments of the present invention, <figref idrefs="DRAWINGS">FIG. 3A</figref> provides a greatly-enlarged partial perspective view of a segment of sheet material <b>52</b> suitable for forming the bag body <b>20</b> as depicted in <figref idrefs="DRAWINGS">FIGS. 1-2</figref>. Materials such as those illustrated and described herein as suitable for use in accordance with the embodiments of the present invention, as well as methods for making and characterizing same, are described in greater detail in commonly-assigned U.S. Pat. Ser. No. 5,518,801, issued to Chappell, et al. on May 21, 1996.

Referring now to <figref idrefs="DRAWINGS">FIG. 3A</figref>, sheet material <b>52</b> includes a “strainable network” of distinct regions. As used herein, the term “strainable network” refers to an interconnected and interrelated group of regions which are able to be extended to some useful degree in a predetermined direction providing the sheet material with an elastic-like behavior in response to an applied and subsequently released elongation. The strainable network includes at least a first region <b>64</b> and a second region <b>66</b>. Sheet material <b>52</b> includes a transitional region <b>65</b> which is at the interface between the first region <b>64</b> and the second region <b>66</b>. The transitional region <b>65</b> will exhibit complex combinations of the behavior of both the first region and the second region. It is recognized that every embodiment of such sheet materials suitable for use in accordance with the present invention will have a transitional region; however, such materials are defined by the behavior of the sheet material in the first region <b>64</b> and the second region <b>66</b>. Therefore, the ensuing description will be concerned with the behavior of the sheet material in the first regions and the second regions only since it is not dependent upon the complex behavior of the sheet material in the transitional regions <b>65</b>.

Sheet material <b>52</b> has a first surface <b>52</b><i>a </i>and an opposing second surface <b>52</b><i>b</i>. In the embodiment shown in <figref idrefs="DRAWINGS">FIG. 3A</figref>, the strainable network includes a plurality of first regions <b>64</b> and a plurality of second regions <b>66</b>. The first regions <b>64</b> have a first axis <b>68</b> and a second axis <b>69</b>, wherein the first axis <b>68</b> is preferably longer than the second axis <b>69</b>. The first axis <b>68</b> of the first region <b>64</b> is substantially parallel to the longitudinal axis “L” of the sheet material <b>52</b> while the second axis <b>69</b> is substantially parallel to the transverse axis “T” of the sheet material <b>52</b>. Preferably, the second axis of the first region, the width of the first region, is from about 0.01 inches to about 0.5 inches and more preferably from about 0.03 inches to about 0.25 inches. The second regions <b>66</b> have a first axis <b>70</b> and a second axis <b>71</b>. The first axis <b>70</b> is substantially parallel to the longitudinal axis of the sheet material <b>52</b>, while the second axis <b>71</b> is substantially parallel to the transverse axis of the sheet material <b>52</b>. Preferably, the second axis of the second region, the width of the second region, is from about 0.01 inches to about 2.0 inches and more preferably from about 0.125 inches to about 1.0 inches. In the embodiment of <figref idrefs="DRAWINGS">FIG. 3A</figref>, the first regions <b>64</b> and the second regions <b>66</b> are substantially linear, extending continuously in a direction substantially parallel to the longitudinal axis of the sheet material <b>52</b>.

The first region <b>64</b> has an elastic modulus E <b>1</b> and a cross-sectional area A <b>1</b>. The second region <b>66</b> has a modulus E <b>2</b> and a cross-sectional area A <b>2</b>.

In the illustrated embodiment, the sheet material <b>52</b> has been “formed” such that the sheet material <b>52</b> exhibits a resistive force along an axis, which in the case of the illustrated embodiment is substantially parallel to the longitudinal axis of the web, when subjected to an applied axial elongation in a direction substantially parallel to the longitudinal axis. As used herein, the term “formed” refers to the creation of a desired structure or geometry upon a sheet material that will substantially retain the desired structure or geometry when it is not subjected to any externally applied elongations or forces. A sheet material of the embodiments of the present invention is comprised of at least a first region and a second region, wherein the first region is visually distinct from the second region. As used herein, the term “visually distinct” refers to features of the sheet material which are readily discernible to the normal naked eye when the sheet material or objects embodying the sheet material are subjected to normal use. As used herein the term “surface-pathlength” refers to a measurement along the topographic surface of the region in question in a direction substantially parallel to an axis. The method for determining the surface-pathlength of the respective regions can be found in the Test Methods section of the above-referenced Chappell et al. patent.

Methods for forming such sheet materials useful in the embodiments of the present invention include, but are not limited to, embossing by mating plates or rolls, thermoforming, high pressure hydraulic forming, or casting. While the entire portion of the web <b>52</b> has been subjected to a forming operation, the present invention may also be practiced by subjecting to formation only a portion thereof, e.g., a portion of the material comprising the bag body <b>20</b>, as will be described in detail below.

In the embodiment shown in <figref idrefs="DRAWINGS">FIG. 3A</figref>, the first regions <b>64</b> are substantially planar. That is, the material within the first region <b>64</b> is in substantially the same condition before and after the formation step undergone by web <b>52</b>. The second regions <b>66</b> include a plurality of raised rib-like elements <b>74</b>. The rib-like elements may be embossed, debossed or a combination thereof. The rib-like elements <b>74</b> have a first or major axis <b>76</b> which is substantially parallel to the transverse axis of the web <b>52</b> and a second or minor axis <b>77</b> which is substantially parallel to the longitudinal axis of the web <b>52</b>. The length parallel to the first axis <b>76</b> of the rib-like elements <b>74</b> is at least equal to, and preferably longer than the length parallel to the second axis <b>77</b>. Preferably, the ratio of the first axis <b>76</b> to the second axis <b>77</b> is at least about 1:1 or greater, and more preferably at least about 2:1 or greater.

The rib-like elements <b>74</b> in the second region <b>66</b> may be separated from one another by unformed areas. Preferably, the rib-like elements <b>74</b> are adjacent one another and are separated by an unformed area of less than 0.10 inches as measured perpendicular to the major axis <b>76</b> of the rib-like elements <b>74</b>, and more preferably, the rib-like elements <b>74</b> are contiguous having essentially no unformed areas between them.

The first region <b>64</b> and the second region <b>66</b> each have a “projected pathlength”. As used herein the term “projected pathlength” refers to the length of a shadow of a region that would be thrown by parallel light. The projected pathlength of the first region <b>64</b> and the projected pathlength of the second region <b>66</b> are equal to one another.

The first region <b>64</b> has a surface-pathlength, L <b>1</b>, less than the surface-pathlength, L <b>2</b>, of the second region <b>66</b> as measured topographically in a direction parallel to the longitudinal axis of the web <b>52</b> while the web is in an untensioned condition. Preferably, the surface-pathlength of the second region <b>66</b> is at least about 15% greater than that of the first region <b>64</b>, more preferably at least about 30% greater than that of the first region, and most preferably at least about 70% greater than that of the first region. In general, the greater the surface-pathlength of the second region, the greater will be the elongation of the web before encountering the force wall. Suitable techniques for measuring the surface-pathlength of such materials are described in the above-referenced Chappell et al. patent.

Sheet material <b>52</b> exhibits a modified “Poisson lateral contraction effect” substantially less than that of an otherwise identical base web of similar material composition. The method for determining the Poisson lateral contraction effect of a material can be found in the Test Methods section of the above-referenced Chappell et al. patent. Preferably, the Poisson lateral contraction effect of webs suitable for use in the present invention is less than about 0.4 when the web is subjected to about 20% elongation. Preferably, the webs exhibit a Poisson lateral contraction effect less than about 0.4 when the web is subjected to about 40, 50 or even 60% elongation. More preferably, the Poisson lateral contraction effect is less than about 0.3 when the web is subjected to 20, 40, 50 or 60% elongation. The Poisson lateral contraction effect of such webs is determined by the amount of the web material which is occupied by the first and second regions, respectively. As the area of the sheet material occupied by the first region increases the Poisson lateral contraction effect also increases. Conversely, as the area of the sheet material occupied by the second region increases the Poisson lateral contraction effect decreases. Preferably, the percent area of the sheet material occupied by the first area is from about 2% to about 90%, and more preferably from about 5% to about 50%.

Sheet materials of the prior art which have at least one layer of an elastomeric material will generally have a large Poisson lateral contraction effect, i.e., they will “neck down” as they elongate in response to an applied force. Web materials useful in accordance with the present invention can be designed to moderate if not substantially eliminate the Poisson lateral contraction effect.

For sheet material <b>52</b>, the direction of applied axial elongation, D, indicated by arrows <b>80</b> in <figref idrefs="DRAWINGS">FIG. 3A</figref>, is substantially perpendicular to the first axis <b>76</b> of the rib-like elements <b>74</b>. The rib-like elements <b>74</b> are able to unbend or geometrically deform in a direction substantially perpendicular to their first axis <b>76</b> to allow extension in web <b>52</b>.

Referring now to <figref idrefs="DRAWINGS">FIG. 3B</figref>, as web of sheet material <b>52</b> is subjected to an applied axial elongation, D, indicated by arrows <b>80</b> in <figref idrefs="DRAWINGS">FIG. 3B</figref>, the first region <b>64</b> having the shorter surface-pathlength, L<b>1</b>, provides most of the initial resistive force, P<b>1</b>, as a result of molecular-level deformation, to the applied elongation. In this stage, the rib-like elements <b>74</b> in the second region <b>66</b> are experiencing geometric deformation, or unbending and offer minimal resistance to the applied elongation. In transition to the next stage, the rib-like elements <b>74</b> are becoming aligned with (i.e., coplanar with) the applied elongation. That is, the second region is exhibiting a change from geometric deformation to molecular-level deformation. This is the onset of the force wall. In the stage seen in <figref idrefs="DRAWINGS">FIG. 3C</figref>, the rib-like elements <b>74</b> in the second region <b>66</b> have become substantially aligned with (i.e., coplanar with) the plane of applied elongation (i.e. the second region has reached its limit of geometric deformation) and begin to resist further elongation via molecular-level deformation. The second region <b>66</b> now contributes, as a result of molecular-level deformation, a second resistive force, P<b>2</b>, to further applied elongation. The resistive forces to elongation provided by both the molecular-level deformation of the first region <b>64</b> and the molecular-level deformation of the second region <b>66</b> provide a total resistive force, PT, which is greater than the resistive force which is provided by the molecular-level deformation of the first region <b>64</b> and the geometric deformation of the second region <b>66</b>.

The resistive force P<b>1</b> is substantially greater than the resistive force P<b>2</b> when (L<b>1</b>+D) is less than L<b>2</b>. When (L<b>1</b>+D) is less than L<b>2</b> the first region provides the initial resistive force P<b>1</b>, generally satisfying the equation: P<b>1</b>=(A<b>1</b>×E<b>1</b>×D)L<b>1</b>

When (L<b>1</b>+D) is greater than L<b>2</b> the first and second regions provide a combined total resistive force PT to the applied elongation, D, generally satisfying the equation: PT=(A<b>1</b>×E<b>1</b>×D)L<b>1</b>+(A<b>2</b>×E<b>2</b>×□L<b>1</b>+D−L<b>2</b>□)L<b>2</b>

The maximum elongation occurring while in the stage corresponding to <figref idrefs="DRAWINGS">FIGS. 3A and 3B</figref>, before reaching the stage depicted in <figref idrefs="DRAWINGS">FIG. 3C</figref>, is the “available stretch” of the formed web material. The available stretch corresponds to the distance over which the second region experiences geometric deformation. The range of available stretch can be varied from about 10% to 100% or more, and can be largely controlled by the extent to which the surface-pathlength L<b>2</b> in the second region exceeds the surface-pathlength L<b>1</b> in the first region and the composition of the base film. The term available stretch is not intended to imply a limit to the elongation which the web of the present invention may be subjected to as there are applications where elongation beyond the available stretch is desirable.

When the sheet material is subjected to an applied elongation, the sheet material exhibits an elastic-like behavior as it extends in the direction of applied elongation and returns to its substantially untensioned condition once the applied elongation is removed, unless the sheet material is extended beyond the point of yielding. The sheet material is able to undergo multiple cycles of applied elongation without losing its ability to substantially recover. Accordingly, the web is able to return to its substantially untensioned condition once the applied elongation is removed.

While the sheet material may be easily and reversibly extended in the direction of applied axial elongation, in a direction substantially perpendicular to the first axis of the rib-like elements, the web material is not as easily extended in a direction substantially parallel to the first axis of the rib-like elements. The formation of the rib-like elements allows the rib-like elements to geometrically deform in a direction substantially perpendicular to the first or major axis of the rib-like elements, while requiring substantially molecular-level deformation to extend in a direction substantially parallel to the first axis of the rib-like elements.

The amount of applied force required to extend the web is dependent upon the composition and cross-sectional area of the sheet material and the width and spacing of the first regions, with narrower and more widely spaced first regions requiring lower applied extensional forces to achieve the desired elongation for a given composition and cross-sectional area. The first axis, (i.e., the length) of the first regions is preferably greater than the second axis, (i.e., the width) of the first regions with a length to width ratio of from about 5:1 or greater.

The depth and frequency of rib-like elements can also be varied to control the available stretch of a web of sheet material suitable for use in accordance with the present invention. The available stretch is increased if for a given frequency of rib-like elements, the height or degree of formation imparted on the rib-like elements is increased. Similarly, the available stretch is increased if for a given height or degree of formation, the frequency of the rib-like elements is increased.

There are several functional properties that can be controlled through the application of such materials to flexible bags of the present invention. The functional properties are the resistive force exerted by the sheet material against an applied elongation and the available stretch of the sheet material before the force wall is encountered. The resistive force that is exerted by the sheet material against an applied elongation is a function of the material (e.g., composition, molecular structure and orientation, etc.) and cross-sectional area and the percent of the projected surface area of the sheet material that is occupied by the first region. The higher the percent area coverage of the sheet material by the first region, the higher the resistive force that the web will exert against an applied elongation for a given material composition and cross-sectional area. The percent coverage of the sheet material by the first region is determined in part, if not wholly, by the widths of the first regions and the spacing between adjacent first regions.

The available stretch of the web material is determined by the surface-pathlength of the second region. The surface-pathlength of the second region is determined at least in part by the rib-like element spacing, rib-like element frequency and depth of formation of the rib-like elements as measured perpendicular to the plane of the web material. In general, the greater the surface-pathlength of the second region the greater the available stretch of the web material.

As discussed above with regard to <figref idrefs="DRAWINGS">FIGS. 3A-3C</figref>, the sheet material <b>52</b> initially exhibits a certain resistance to elongation provided by the first region <b>64</b> while the rib-like elements <b>74</b> of the second region <b>66</b> undergo geometric motion. As the rib-like elements transition into the plane of the first regions of the material, an increased resistance to elongation is exhibited as the entire sheet material then undergoes molecular-level deformation. Accordingly, sheet materials of the type depicted in <figref idrefs="DRAWINGS">FIGS. 3A-3C</figref> and described in the above-referenced Chappell et al. patent provide the performance advantages of the present invention when formed into closed containers such as the flexible bags of the present invention.

An additional benefit realized by the utilization of the aforementioned sheet materials in constructing flexible bags according to the present invention is the increase in visual and tactile appeal of such materials. Polymeric films commonly utilized to form such flexible polymeric bags are typically comparatively thin in nature and frequently have a smooth, shiny surface finish. While some manufacturers utilize a small degree of embossing or other texturing of the film surface, at least on the side facing outwardly of the finished bag, bags made of such materials still tend to exhibit a slippery and flimsy tactile impression. Thin materials coupled with substantially two-dimensional surface geometry also tend to leave the consumer with an exaggerated impression of the thinness, and perceived lack of durability, of such flexible polymeric bags.

In contrast, sheet materials useful in accordance with the present invention such as those depicted in <figref idrefs="DRAWINGS">FIGS. 3A-3C</figref> exhibit a three-dimensional cross-sectional profile wherein the sheet material is (in an un-tensioned condition) deformed out of the predominant plane of the sheet material. This provides additional surface area for gripping and dissipates the glare normally associated with substantially planar, smooth surfaces. The three-dimensional rib-like elements also provide a “cushiony” tactile impression when the bag is gripped in one's hand, also contributing to a desirable tactile impression versus conventional bag materials and providing an enhanced perception of thickness and durability. The additional texture also reduces noise associated with certain types of film materials, leading to an enhanced aural impression.

Suitable mechanical methods of forming the base material into a web of sheet material suitable for use in the present invention are well known in the art and are disclosed in the aforementioned Chappell et al. patent and commonly-assigned U.S. Pat. Ser. No. 5,650,214, issued Jul. 22, 1997 in the names of Anderson et al.

Another method of forming the base material into a web of sheet material suitable for use in the present invention is vacuum forming. An example of a vacuum forming method is disclosed in commonly assigned U.S. Pat. Ser. No. 4,342,314, issued to Radel et al. on Aug. 3, 1982. Alternatively, the formed web of sheet material may be hydraulically formed in accordance with the teachings of commonly assigned U.S. Pat. Ser. No. 4,609,518 issued to Curro et al. on Sep. 2, 1986.

The method of formation can be accomplished in a static mode, where one discrete portion of a base film is deformed at a time. Alternatively, the method of formation can be accomplished using a continuous, dynamic press for intermittently contacting the moving web and forming the base material into a formed web material of the present invention. These and other suitable methods for forming the web material of the present invention are more fully described in the above-referenced Chappell et al. patent. The flexible bags may be fabricated from formed sheet material or, alternatively, the flexible bags may be fabricated and then subjected to the methods for forming the sheet material.

Referring now to <figref idrefs="DRAWINGS">FIG. 4</figref>, other patterns for first and second regions may also be employed as sheet materials <b>52</b> suitable for use in accordance with the present invention. The sheet material <b>52</b> is shown in <figref idrefs="DRAWINGS">FIG. 4</figref> in its substantially untensioned condition. The sheet material <b>52</b> has two centerlines, a longitudinal centerline, which is also referred to hereinafter as an axis, line, or direction “L” and a transverse or lateral centerline, which is also referred to hereinafter as an axis, line, or direction “T”. The transverse centerline “T” is generally perpendicular to the longitudinal centerline “L”. Materials of the type depicted in <figref idrefs="DRAWINGS">FIG. 4</figref> are described in greater detail in the aforementioned Anderson et al. patent.

As discussed above with regard to <figref idrefs="DRAWINGS">FIGS. 3A-3C</figref>, sheet material <b>52</b> includes a “strainable network” of distinct regions. The strainable network includes a plurality of first regions <b>60</b> and a plurality of second regions <b>66</b> which are visually distinct from one another. Sheet material <b>52</b> also includes transitional regions <b>65</b> which are located at the interface between the first regions <b>60</b> and the second regions <b>66</b>. The transitional regions <b>65</b> will exhibit complex combinations of the behavior of both the first region and the second region, as discussed above.

Sheet material <b>52</b> has a first surface, (facing the viewer in <figref idrefs="DRAWINGS">FIG. 4</figref>), and an opposing second surface (not shown). In the embodiment shown in <figref idrefs="DRAWINGS">FIG. 4</figref>, the strainable network includes a plurality of first regions <b>60</b> and a plurality of second regions <b>66</b>. A portion of the first regions <b>60</b>, indicated generally as <b>61</b>, are substantially linear and extend in a first direction. The remaining first regions <b>60</b>, indicated generally as <b>62</b>, are substantially linear and extend in a second direction which is substantially perpendicular to the first direction. The first direction may be perpendicular to the second direction. Other angular relationships between the first direction and the second direction may be suitable so long as the first regions <b>61</b> and <b>62</b> intersect one another. The angle between the first and second directions ranges from about 45° to about 135°. In one embodiment the angle is about 90°. The intersection of the first regions <b>61</b> and <b>62</b> forms a boundary, indicated by phantom line <b>63</b> in <figref idrefs="DRAWINGS">FIG. 4</figref>, which completely surrounds the second regions <b>66</b>.

In one embodiment the width <b>68</b> of the first regions <b>60</b> may be from about 0.01 inches to about 0.5 inches. In another embodiment the width <b>68</b> of the first regions <b>60</b> may be from about 0.03 inches to about 0.25 inches. However, other width dimensions for the first regions <b>60</b> may be suitable. Because the first regions <b>61</b> and <b>62</b> are perpendicular to one another and equally spaced apart, the second regions have a square shape. However, other shapes for the second region <b>66</b> are suitable and may be achieved by changing the spacing between the first regions and/or the alignment of the first regions <b>61</b> and <b>62</b> with respect to one another. The second regions <b>66</b> have a first axis <b>70</b> and a second axis <b>71</b>. The first axis <b>70</b> is substantially parallel to the longitudinal axis of the web material <b>52</b>, while the second axis <b>71</b> is substantially parallel to the transverse axis of the web material <b>52</b>. The first regions <b>60</b> have an elastic modulus E <b>1</b> and a cross-sectional area A <b>1</b>. The second regions <b>66</b> have an elastic modulus E <b>2</b> and a cross-sectional area A <b>2</b>.

In the embodiment shown in <figref idrefs="DRAWINGS">FIG. 4</figref>, the first regions <b>60</b> are substantially planar. That is, the material within the first regions <b>60</b> is in substantially the same condition before and after the formation step undergone by web <b>52</b>. The second regions <b>66</b> include a plurality of raised rib-like elements <b>74</b>. The rib-like elements <b>74</b> may be embossed, debossed or a combination thereof. The rib-like elements <b>74</b> have a first or major axis <b>76</b> which is substantially parallel to the longitudinal axis of the web <b>52</b> and a second or minor axis <b>77</b> which is substantially parallel to the transverse axis of the web <b>52</b>.

The rib-like elements <b>74</b> in the second region <b>66</b> may be separated from one another by unformed areas, essentially unembossed or debossed, or simply formed as spacing areas. Preferably, the rib-like elements <b>74</b> are adjacent one another and are separated by an unformed area of less than 0.10 inches as measured perpendicular to the major axis <b>76</b> of the rib-like elements <b>74</b>, and more preferably, the rib-like elements <b>74</b> are contiguous having essentially no unformed areas between them.

The first regions <b>60</b> and the second regions <b>66</b> each have a “projected pathlength”. As used herein the term “projected pathlength” refers to the length of a shadow of a region that would be thrown by parallel light. The projected pathlength of the first region <b>60</b> and the projected pathlength of the second region <b>66</b> are equal to one another.

The first region <b>60</b> has a surface-pathlength, L<b>1</b>, less than the surface-pathlength, L<b>2</b>, of the second region <b>66</b> as measured topographically in a parallel direction while the web is in an untensioned condition. Preferably, the surface-pathlength of the second region <b>66</b> is at least about 15% greater than that of the first region <b>60</b>, more preferably at least about 30% greater than that of the first region, and most preferably at least about 70% greater than that of the first region. In general, the greater the surface-pathlength of the second region, the greater will be the elongation of the web before encountering the force wall.

For sheet material <b>52</b>, the direction of applied axial elongation, D, indicated by arrows <b>80</b> in <figref idrefs="DRAWINGS">FIG. 4</figref>, is substantially perpendicular to the first axis <b>76</b> of the rib-like elements <b>74</b>. This is due to the fact that the rib-like elements <b>74</b> are able to unbend or geometrically deform in a direction substantially perpendicular to their first axis <b>76</b> to allow extension in web <b>52</b>.

Referring now to <figref idrefs="DRAWINGS">FIG. 5</figref>, as web <b>52</b> is subjected to an applied axial elongation, D, indicated by arrows <b>80</b> in <figref idrefs="DRAWINGS">FIG. 5</figref>, the first regions <b>60</b> having the shorter surface-pathlength, L<b>1</b>, provide most of the initial resistive force, P<b>1</b>, as a result of molecular-level deformation, to the applied elongation which corresponds to stage I. While in stage I, the rib-like elements <b>74</b> in the second regions <b>66</b> are experiencing geometric deformation, or unbending and offer minimal resistance to the applied elongation. In addition, the shape of the second regions <b>66</b> changes as a result of the movement of the reticulated structure formed by the intersecting first regions <b>61</b> and <b>62</b>. Accordingly, as the web <b>52</b> is subjected to the applied elongation, the first regions <b>61</b> and <b>62</b> experience geometric deformation or bending, thereby changing the shape of the second regions <b>66</b>. The second regions are extended or lengthened in a direction parallel to the direction of applied elongation, and collapse or shrink in a direction perpendicular to the direction of applied elongation.

In addition to the aforementioned elastic-like properties, a sheet material of the type depicted in <figref idrefs="DRAWINGS">FIGS. 4 and 5</figref> is believed to provide a softer, more cloth-like texture and appearance, and is more quiet in use.

Various compositions suitable for constructing the flexible bags of embodiments of the present invention include substantially impermeable materials such as polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyethylene (PE), polypropylene (PP), aluminum foil, coated waxed, etc.) and uncoated paper, coated nonwovens etc., and substantially permeable materials such as scrims, meshes, wovens, nonwovens, or perforated or porous films, whether predominantly two-dimensional in nature or formed into three-dimensional structures. Such materials may comprise a single composition or layer or may be a composite structure of multiple materials.

Once the desired sheet materials are manufactured in any desirable and suitable manner, comprising all or part of the materials to be utilized for the bag body, the bag may be constructed in any known and suitable fashion such as those known in the art for making such bags in commercially available form. Heat, mechanical, or adhesive sealing technologies may be utilized to join various components or elements of the bag to themselves or to each other. In addition, the bag bodies may be thermoformed, blown, or otherwise molded rather than reliance upon folding and bonding techniques to construct the bag bodies from a web or sheet of material. Two recent U.S. patents which are illustrative of the state of the art with regard to flexible storage bags similar in overall structure to those depicted in <figref idrefs="DRAWINGS">FIGS. 1 and 2</figref> but of the types currently available are U.S. Pat. Ser. No. 5,554,093, issued Sep. 10, 1996 to Porchia et al., and U.S. Pat. Ser. No. 5,575,747, issued Nov. 19, 1996 to Dais et al.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”.

All documents cited in the Detailed Description of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.